Sequential cooling insert for turbine stator vane

ABSTRACT

A sequential impingement cooling insert for a turbine stator vane that forms a double impingement for the pressure and suction sides of the vane or a triple impingement. The insert is formed from a sheet metal formed in a zigzag shape that forms a series of alternating impingement cooling channels with return air channels, where pressure side and suction side impingement cooling plates are secured over the zigzag shaped main piece. Another embodiment includes the insert formed from one or two blocks of material in which the impingement channels and return air channels are machined into each block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit to Provisional Patent Application61/725,507 filed on Nov. 13, 2012 and entitled SEQUENTIAL COOLING INSERTFOR TURBINE STATOR VANE.

FEDERAL RESEARCH STATEMENT

This invention was made with Government support under contract numberDE-FE-0006696 awarded by Department of Energy. The Government hascertain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a gas turbine engine, andmore specifically to a turbine stator vane with sequential impingementcooling.

2. Description of the Related Art Including Information Disclosed Under37 CFR 1.97 and 1.98

In a gas turbine engine, air is first compressed to a high pressure in acompressor. The high pressure air is then mixed with fuel and burned atnearly constant pressure in the combustor. The high temperature gasexhausted from the combustor is then expanded through a turbine whichthen drives the compressor. If executed correctly, the exhaust streamfrom the turbine maintains sufficient energy to provide useful work byforming a jet, such as in aircraft jet propulsion or through expansionin another turbine which may then be used to drive a generator likethose used in electrical power generation. The efficiency and poweroutput from these machines will depend on many factors including thesize, pressure and temperature levels achieved and an agglomeration ofthe efficiency levels achieved by each of the individual components.

Current turbine components are cooled by circulating relatively (to thegas turbine engine) cool air, which is extracted from the compressor,within passages located inside the component to provide a convectivecooling effect. In many recent arrangements, the spent cooling flow isdischarged onto the surfaces of the component to provide an additionalfilm cooling effect.

The challenge to cool first stage turbine vanes (these are exposed tothe highest temperature gas flow), in particular, is complicated by thefact that the pressure differential between the vane cooling air and thehot gas which flows around the airfoil must necessarily be small toachieve high efficiency. Specifically, coolant for the first stageturbine vane is derived from the compressor discharge, while the hot gasis derived from the combustor exit flow stream. The pressuredifferential available for cooling is then defined by the extremelysmall pressure drop which occurs in the combustor. This is because thepressure of the coolant supplied to the vane is only marginally higherthan the pressure of the hot gas flowing around the airfoil as definedby the combustor pressure loss, which is desirably small. This pressuredrop is commonly on the order of only a few percentage points. Further,it is desirable to maintain coolant pressure inside the vane higher thanthe pressure in the hot gas flow path to insure coolant will always flowout of the vane and not hot gas into the vane. Conversely, in the eventhot gas is permitted to flow into the vane, serious material damage canresult as the materials are heated beyond their capabilities andprogression to failure will be swift. As a consequence, current firststage turbine vanes are typically cooled using a combination of internalconvection heat transfer using single impingement at very low pressureratio, while spent coolant is ejected onto the airfoil surface toprovide film cooling.

The efficiency of the convective cooling system is measured by theamount of coolant heat-up divided by the theoretical heat-up possible.In the limits, little coolant heat-up reflects low cooling efficiencywhile heating the coolant to the temperature of the surface to be cooled(a theoretical maximum) yields 100% cooling efficiency. In the previousmethods using single impingement, the flow could only be used once toimpinge on the surface to be cooled. This restriction precludes theability to heat the coolant substantially, thereby limiting the coolingefficiency.

U.S. Pat. No. 8,096,766 issued to Downs on Jan. 17, 2012 and entitledAIR COOLED TURBINE AIRFOIL WITH SEQUENTIAL COOLING discloses one suchinsert having sequential cooling where the insert is build up from astack of alternating plates that are bonded together in chordwiseplanes. This insert provides for the sequential cooling of the vanewalls but is a very expensive insert because of the numerous plates thatmust be individually machined and then bonded together.

BRIEF SUMMARY OF THE INVENTION

A sequential cooling insert for a turbine stator vane, where the insertis formed from a zigzag shaped main piece that forms a series ofalternating impingement cooling air channels and return air channels. Apressure side wall and a suction side wall are secured over the zigzagshaped main piece to enclose the channels. The pressure and suction sidewalls include rows of impingement cooling air holes and return air holesto form the series of first and second impingement cooling for the vaneairfoil.

In a second embodiment, the insert is formed from a pressure sidesection and a section side section bonded together, where the pressureside section includes spanwise extending rows of impingement channelsalternating between spanwise extending rows of return air channels. Thesuction side section includes chordwise extending rows of impingementchannels alternating between rows of return air channels. Thisembodiment forms a triple impingement with a first impingement on thepressure side, a second impingement on an aft side of the suction side,and a third impingement on a forward side of the suction side of theinsert.

Another insert includes a triple impingement in which the insert isformed from one or two blocks of material in which the impingementchannels and return air channels are machined into the block or blocks.In one embodiment, the pressure side wall and suction side wall havingthe impingement cooling holes and return air holes are bonded over themachined section. In another embodiment, the impingement holes andreturn air holes are drilled into the machined sections.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a top view of a sequential cooling insert according to afirst embodiment of the present invention.

FIG. 2 shows a front view of the insert of FIG. 1.

FIG. 3 shows a side view of the insert of FIG. 1.

FIG. 4 shows a cross section cut of the insert through line A-A in FIG.3.

FIG. 5 shows a cross section cut of the insert through line B-B in FIG.3.

FIG. 6 shows a cross section cut of the insert through line C-C in FIG.3.

FIG. 7 shows an exploded view of the insert of FIG. 1 in all its pieces.

FIG. 8 shows a top view of a sequential cooling insert according to asecond embodiment of the present invention.

FIG. 9 shows a front view of the insert of FIG. 8.

FIG. 10 shows a side view of the insert of FIG. 8.

FIG. 11 shows a cross section cut of the insert through line A-A in FIG.10.

FIG. 12 shows a cross section cut of the insert through line B-B in FIG.10.

FIG. 13 shows a cross section cut of the insert through line C-C in FIG.10.

FIG. 14 shows an exploded view of the insert of FIG. 8 in all itspieces.

FIG. 15 shows a top view of a sequential cooling insert according to athird embodiment of the present invention.

FIG. 16 shows a front view of the insert of FIG. 15.

FIG. 17 shows a side view of the insert of FIG. 15.

FIG. 18 shows a cross section cut of the insert through line A-A in FIG.17.

FIG. 19 shows a cross section cut of the insert through line B-B in FIG.17.

FIG. 20 shows a cross section cut of the insert through line C-C in FIG.17.

FIG. 21 shows an exploded view of the insert of FIG. 15 in all itspieces.

FIG. 22 shows a top view of a sequential cooling insert according to afourth embodiment of the present invention.

FIG. 23 shows a front view of the insert of FIG. 22.

FIG. 24 shows a side view of the insert of FIG. 22.

FIG. 25 shows a cross section cut through line A-A of the insert in FIG.24.

FIG. 26 shows a cross section cut through line B-B of the insert in FIG.24.

FIG. 27 shows an exploded view of the insert of FIG. 22 in all of itspieces.

FIG. 28 shows a top view of a sequential cooling insert according to afifth embodiment of the present invention.

FIG. 29 shows a front view of the insert of FIG. 28.

FIG. 30 shows a side view of the insert of FIG. 28.

FIG. 31 shows a cross section cut through line A-A of the insert in FIG.30.

FIG. 32 shows a cross section cut through line B-B of the insert in FIG.30.

FIG. 33 shows a cross section cut through line C-C of the insert in FIG.30.

FIG. 34 shows an exploded view of the insert of FIG. 28 in all of itspieces.

FIG. 35 shows a top view of a sequential cooling insert according to asixth embodiment of the present invention.

FIG. 36 shows a front view of the insert of FIG. 35 through line D-D inFIG. 37.

FIG. 37 shows a side view of the insert of FIG. 35.

FIG. 38 shows a cross section cut through line A-A of the insert in FIG.37.

FIG. 39 shows a cross section cut through line B-B of the insert in FIG.37.

FIG. 40 shows a cross section cut through line C-C of the insert in FIG.37.

FIG. 41 shows an exploded view of the insert of FIG. 28 in all of itspieces.

FIG. 42 shows a side view of the insert from angle E in FIG. 41.

FIG. 43 shows a side view of the insert from angle F in FIG. 41.

FIG. 44 shows a top view of a sequential cooling insert according to aseventh embodiment of the present invention.

FIG. 45 shows a front view of the insert of FIG. 44.

FIG. 46 shows a side view of the insert of FIG. 44.

FIG. 47 shows a cross section cut through line A-A of the insert in FIG.46.

FIG. 48 shows a cross section cut through line B-B of the insert in FIG.46.

FIG. 49 shows a cross section cut through line C-C of the insert in FIG.46.

FIG. 50 shows a cross section cut through line D-D of the insert in FIG.46.

FIG. 51 shows an exploded view of the insert of FIG. 44 in all of itspieces.

FIG. 52 shows a side view of the insert of FIG. 44 from an angle F inFIG. 51.

FIG. 53 shows a side view of the insert of FIG. 44 from an angle G inFIG. 51.

FIG. 54 shows a side view of the insert of FIG. 44 from an angle H inFIG. 51.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an insert for use in a hollow turbine statorvane to provide impingement cooling of the backside surfaces of thewalls of the vane using a sequential impingement cooling circuit formedwithin the insert. The insert of the present invention is a much simplerdesign than the prior art Downs AIR COOLED TURBINE AIRFOIL WITHSEQUENTIAL COOLING design and thus can be made much cheaper and withfewer pieces. The sequential cooling insert of the present invention isintended for use in a large frame heavy duty industrial gas turbineengine for the first stage stator vanes, but could be used in smalleraero engines as well. FIGS. 1-7 show various views of a first embodimentof the sequential cooling insert. FIG. 1 shows a top view of an inletcover plate 11 with cooling air supply openings 12 and two seal grooves13 for radial extending seals. The inlet cover plate 11 is secured to atop side of the insert and is welded to an outer endwall of the vane.FIG. 2 shows a side view of an insert 15 with the inlet cover plate 11and a bottom cap 16 secured to a bottom side of the insert 11 thatslides within a cap receiver 17 welded or bonded to an inner endwall ofthe vane. FIG. 3 shows a side view of the insert 15 with rows ofimpingement cooling air holes (smaller holes) and rows of return airholes (larger holes).

FIG. 4 shows a cross section view from a top direction of the featuresof the insert that includes a passage divider 21 with a suction sideimpingement plate 23 bonded to a suction side of the passage divider 21and a pressure side impingement plate 22 bonded to a pressure side ofthe divider plate 21. Two seal grooves 24 and 25 are bonded to theinsert in alignment with the seal grooves 13 and 14 in the inlet coverplate 11 to receive the radial extending seals. The divider plate 21 isa one piece divider plate bent into a zigzag shape to form alternatingchannels of impingement cooling air channels (a) and return air channels(b). The impingement cooling air channels (a) are connected directly tothe cooling air supply openings 12 formed in the inlet cover plate 11. Arow of impingement cooling air holes is formed on the pressure side ofthe insert in the divider plate 21 and the pressure side impingementplate 22 that discharge impingement cooling air from the impingementcooling air channels (a) against the pressure side wall of the vane.

FIG. 5 shows another view of the insert with the return air coolingholes formed in the pressure side impingement plate 22 that open intothe return air cooling channels (b). FIG. 6 shows another view of theinsert with the suction side impingement plate 23 having rows ofimpingement cooling holes connected to the return air cooling channels(b) that discharge impingement cooling air to the backside surface ofthe suction side wall of the vane.

FIG. 7 shows an exploded view of the insert of the first embodiment. Thepressure side impingement plate 22 bonded to the divider plate 21includes spanwise extending rows of impingement cooling holes (smallerholes) and larger return air holes. The divider plate 21 is welded orbonded to the inlet cover plate 11, and the inlet cover plate 11 iswelded or bonded to the vane outer endwall to secure the insert to thehollow section of the vane. The bottom cap 16 includes a slot 18 on thebottom side that slides over a rail 19 formed on an inner side of thecap receiver 17 welded or bonded to the vane inner endwall. The slot 18and the rail 19 allow for the insert and the cap receiver 17 to expandand contract in a radial or spanwise direction of the vane due tothermal growth between the vane and the insert. The insert is thusformed from three major pieces that include the divider plate 21 and theP/S and S/S impingement plates 22 and 23. The inlet cover plate 11 willalso close off the return air channels (b) so that the return coolingair will flow through the impingement cooling holes formed within theS/S impingement plate 22.

The insert is assembled and then placed within the hollow vane airfoilwith the inlet cover plate 11 welded or bonded to the vane outer endwallto secure the insert within the vane. with the insert secured within thevane, two radial extending seals are insert into the seal grooves 24 and25 through the seal openings 13 and 14 formed in the inlet cover plate11, and then the openings 13 and 14 are closed by plugs to secure theseals in place. Cooling air supplied to the cooling air supply openings12 will flow into the impingement cooling air channels (a) as seen inFIG. 4 to produce impingement cooling for the P/S surface of the vane,then collect and flow through the return air holes and into the returnair channels (b) as seen in FIG. 5, and then flow through theimpingement cooling holes formed in the S/S impingement plate (FIG. 6)to produce impingement cooling for the S/S wall of the vane. Spentimpingement cooling air for the S/S wall is collected and directed toflow out from the vane through a row of exit holes in the trailing edgeor exit slots formed on a pressure side wall in the trailing edge regionof the vane.

The insert of FIGS. 1-7 has the P/S impingement plate 22 and the S/Simpingement plate 23 welded or bonded to the divider plate 21, and thenthe impingement cooling holes and return air holes are drilled into theplates. In the FIGS. 1-7 embodiment, the impingement holes on the P/Sand S/S impingement plates are drilled through two plates: the P/Simpingement plate 22 and the divider plate 21 on the P/S and the S/Simpingement plate 23 and the divider plate 21 on the S/S of the insert.The insert of FIGS. 1-7 provides for a series flow of impingementcooling air with the pressure side wall cooled first followed by thesuction side wall using the same cooling air flow.

FIGS. 8 through 14 show a second embodiment of the sequential coolinginsert of the present invention. The inlet cover plate 11 is similar tothat of the FIG. 1 embodiment. A divider plate 26 is similar to thedivider plate 21 in the FIG. 4 embodiment with a P/S impingement plate22 and a S/S impingement plate 23 welded or bonded to the sides.However, the divider plate 26 in FIG. 11 is shaped so that a bondingsurface 25 between the divider plate 21 and the two impingement plates22 and 23 is much wider than in the FIG. 4 embodiment. The bondingsurface 25 is the location where the impingement holes are drilledthrough the two plates on the P/S and the S/S. the impingement coolingair supply channels (a) in the FIG. 11 embodiment are diverging towardthe impingement holes, while in the FIG. 4 embodiment the impingementsupply channels (a) are diverging. This is the difference between thefirst embodiment of FIGS. 1-7 and the second embodiment of FIGS. 8-14.

FIG. 14 shows an exploded view of the insert of the second embodimentwith the divider plate 26 having the impingement holes formed on thewider surface 25 that forms the bonding surface for the impingementplates 22 and 23. Cooling air supplied through the inlet cover plateopenings 12 flows into the impingement cooling air supply channels (a)and then through the impingement cooling air holes on the P/S, thenflows into the return air channels (b) and then through the S/Simpingement cooling air holes.

FIGS. 15 through 21 show a third embodiment of the present inventionwith a divider plate 27 having the P/S impingement plate 22 and a S/Simpingement plate 23 welded or bonded to the surfaces. In the FIG. 18embodiment, the divider plate 27 is shaped such that the impingementcooling holes on the P/S and the S/S impingement plates only need to bedrilled through one plate and not through two plates like in the FIG. 4and FIG. 11 embodiments. The return air holes (larger holes) are stilldrilled through two plates in the insert. Impingement supply channels(a) are shown in FIG. 19 with impingement cooling holes directed to theP/S, and the return air channels (b) are shown in FIG. 18 withimpingement cooling holes directed to discharge to the S/S wall of thevane. in the FIG. 19 embodiment, the impingement cooling holes on theP/S and the S/S are located at an end of a converging channel (a) or (b)and the impingement holes are formed in only one plate. Also, in thisembodiment the bonding surface for the impingement plates 22 and 23 onthe divider plate 27 is a larger surface area. Thus, the FIG. 21 insertis stronger than the other two inserts.

A fourth embodiment of the insert is shown in FIGS. 22 through 27 andforms not a double or two series of impingement but triple or threeseries of impingement. The inlet cover plate 11 includes three sealgrooves 13 instead of two as in earlier embodiments. FIG. 25 shows a cutthrough the insert with impingement cooling air supply channels formedon a P/S of the insert for the entire pressure side wall of the vanewith return air channels spaced in-between. Spent impingement coolingair form the P/S wall flows through the return air channels and into acollection cavity formed on the S/S part of the insert as seen in FIG.26 and then flows out through impingement cooling holes (b) for coolingan aft section of the vane on the suction side wall. Cooling air from(b) flows into a second collection cavity in FIG. 25 and then flowsthrough impingement cooling holes (c) on a forward section of the S/Swall to provide impingement cooling here. Thus, in the FIGS. 22 through27 embodiment of the insert, the P/S wall is cooled first withimpingement cooling air, then the aft section of the S/S wall with thesame cooling air, and then the forward section of the S/S wall with thesame cooling air in series by the insert.

FIG. 27 shows an exploded view of the complex assembly of the fourthembodiment of the insert. A main body of the insert is formed from aseries of spanwise extending pieces that includes a return plenum piece31, an impingement supply piece 32, and a vertical divider sheet 33. Thereturn plenum piece 31 has slots formed on one side on the P/S side thatforms return air holes when bonded to the divider sheet 33. Theimpingement supply piece 32 includes impingement holes drilled into theP/S side of the piece. An alternating arrangement of these pieces arebonded together to form the P/S section of the insert with theimpingement holes and return holes for the pressure side of the insert.

The suction side wall of the insert is formed by a series of chordwiseextending pieces that include a S/S secondary impingement chamber piece34 with impingement holes 35, a S/S tertiary impingement chamber piece37 with impingement holes 35 and return air holes 38, and horizontaldivider sheets 36 stacked in an alternating arrangement to form thesecond and third impingement chambers for the suction side wall of thevane. All of the pieces that form the impingement holes and retrun holesfor the pressure side and the suction side walls of the vane are bondedtogether to form a single piece insert.

In the insert of FIGS. 22 through 27, cooling air flows through theopenings in the inlet cover plate 11 and down through the impingementcooling air supply channels extending in a spanwise direction andthrough the rows of first impingement holes to provide impingementcooling for the entire P/S wall of the vane. the spent first impingementcooling air then flows through the rows of larger return air holesformed on the P/S section of the insert and then into the collectionchambers formed by the S/S secondary impingement plates 34 where thecooling air then flows through the second impingement cooling holes 35to provide cooling for an aft section of the S/S wall. The spend secondimpingement cooling air then flows through the return air holes 38formed by the tertiary impingement plates 37 and then through the thirdimpingement cooling holes 35 to provide impingement cooling for theforward section of the S/S wall of the vane. The spent third impingementcooling air can then flow out from the vane through an arrangement offilm cooling holes formed on the vane airfoil in this section of thevane.

A fifth embodiment of the insert is shown in FIGS. 28 through 34 and issimilar to the fourth embodiment shown in FIG. 27 with three impingementlocations in series. The fifth embodiment in FIG. 34 includes a dividerplate 44 with cross-over holes secured between the P/S section of theinsert and the S/S section. The FIG. 34 embodiment includes a returnplenum piece 41 with slots to form the return air holes and animpingement supply piece 42 having an L-shape with impingement coolingholes formed on the side facing the P/S wall. A divider sheet 33 is usedto separate both pieces 41 and 42.

The suction wall side of the insert is formed by the same chordwiseextending pieces as in the FIG. 27 embodiment but with an addition ofthe divider plate 44 with the cross-over holes. The stacks of spanwiseextending pieces on the P/S and the chordwise extending pieces on theS/S and the divider plate 44 are bonded together to form the singlepiece insert. Cooling supply air flows through the openings in the inletcover plate 11 and into the spanwise extending impingement cooling airsupply channels on the P/S and through the first impingement coolingholes to cool the P/S of the vane. The spent first impingement coolingair then flows through the rows of spanwise extending return airchannels and into the collection cavities formed on the S/S section ofthe insert through the cross-over holes in the divider plate 44 and thenthrough the second impingement cooling holes to cool the aft side of theS/S wall. The second impingement cooling air then flows through thereturn air holes 38 and then through the third impingement cooling holes35 to provide cooling for the forward section of the S/S wall of thevane.

A sixth embodiment of the insert is shown in FIGS. 35 through 41 and issimilar to the fourth and fifth embodiments in that a series of threeimpingements occur. The sixth embodiment of FIG. 41 is not formed with astack of pieces bonded together but from a single piece machined withthe impingement channels and return air channels formed therein. Onepiece 51 is machined on the P/S and the S/S with the spanwise extendingfeed slots 52 and the return air channels 53 on the P/S and with thechordwise extending feed channels and return air channels on the S/S ofthe insert. The P/S impingement plate 54 and the aft and forward S/Simpingement plate 55 and 56 are then bonded over the main insert piece51 to enclose the channels. The impingement plates 54 and 55 that formthe impingement and return holes for the P/S of the vane and the aftsection on the S/S include both impingement holes and return air holes,while the forward S/S impingement plate 56 includes only impingementcooling holes. The flow through the insert of FIG. 41 works the same asin the FIGS. 27 and 34 embodiments.

FIG. 42 shows a side view of the insert on the S/S side with the chordwise extending impingement supply channels and return air channelsalternating along the insert. FIG. 43 shows a side view of the insertfrom the P/S side with the spanwise extending impingement supplychannels and the return air channels alternating. Return air holes areshown in both FIGS. 42 and 43 views. The impingement holes are formed bythe impingement plates bonded over the return air holes.

FIGS. 44 through 54 shows a seventh embodiment of the insert and alsoincludes a series of three impingement cooling surfaces connected inseries. In this FIG. 51 embodiment, the insert is formed with a P/S mainpiece 61 and a S/S main piece 64 both having the supply and returnchannels formed therein by machining and the impingement holes andreturn holes drilled into them. The P/S main piece 61 includes thespanwise extending feed holes 62 with the impingement holes and returnair holes drilled from the P/S surface to the feed holes or return airchannels. A divider plate 63 with cross-over holes is secured betweenthe P/S piece 61 and the S/S piece 64. The S/S piece 64 includes thechordwise extending impingement supply channels and the return airchannels machined into the S/S face.

FIG. 52 shows the outside surface of the P/S piece with the spanwiseextending return air channels and return air holes. FIG. 53 shows theinside surface of the S/S piece with the chordwise extending channelsthat include channels with return holes and impingement holes for thesecond impingement section of the vane and channels with onlyimpingement holes for the third impingement section of the vane. FIG. 54shows an external surface of the S/S surface of the insert 64 with theimpingement holes and return holes for the aft section on the left sideand the impingement holes for the forward section of the S/S wall of thevane on the right side of this figure.

The insert represented by FIG. 51 receives cooling air from openings inthe inlet cover plate that then flows into the spanwise extendingimpingement cooling supply channels on the P/S of the insert, thenthrough the impingement cooling holes for the first impingement on theentire P/S wall of the vane. the spent first impingement cooling airthen flows into the spanwise extending return air channels and throughthe cross-over holes in the divider plate 63 and into the chordwiseextending impingement supply channels on the S/S side of the insert.This cooling air then flows through the second impingement cooling holesformed on the aft section of the S/S wall and then into the return airchannels, where the cooling air then flows through the third series ofimpingement cooling air holes in the forward section of the S/S wall ofthe vane.

We claim the following:
 1. An impingement cooling insert for a turbinestator vane of a gas turbine engine, the impingement cooling insertcomprising: a zigzag shaped main piece forming an alternating series ofimpingement cooling air channels and return air channels extending in aspanwise direction of a stator vane airfoil; a pressure side wallsecured to a pressure side of the zigzag shaped main piece; a suctionside wall secured to a suction side of the zigzag shaped main piece; aninlet cover plate secured to a top side of the zigzag shaped main piece;the top cover plate having cooling air supply openings that connect tothe impingement cooling air channels; a bottom cap secured to a bottomside of the zigzag shaped main piece to block off the impingementcooling air channels and the return air channels; a row of impingementcooling air holes formed in the pressure side wall and connected to theimpingement cooling air channels; a row of return air holes formed inthe pressure side wall and connected to the return air channels; and, arow of impingement cooling air holes formed in the suction side wall andconnected to the return air channels.
 2. The impingement cooling insertof claim 1, and further comprising: the zigzag shaped main piece hasflat surfaces on the pressure side and the suction side that formbonding surfaces for the pressure side wall and the suction side wall.3. The impingement cooling insert of claim 1, and further comprising:the zigzag shaped main piece forms converging shaped impingement coolingair channels and converging shaped return air channels in a direction ofcooling air flow.
 4. The impingement cooling insert of claim 1, andfurther comprising: the bottom cap includes a slot on a bottom side; abottom cap receiver to be secured to an inner endwall of the statorvane; ahe bottom cap receiver includes a rail on a top side that slideswithin the slot of the bottom cap to allow for a radial displacement ofthe bottom cap within the bottom cap receiver.
 5. The impingementcooling insert of claim 1, and further comprising: the zigzag shapedmain piece forms diverging shaped impingement cooling air channels anddiverging shaped return air channels in a direction of cooling air flow.6. The impingement cooling insert of claim 3, and further comprising:the rows of impingement cooling air holes are formed in the pressureside wall and the suction side wall and not in the zigzag shaped mainpiece; and, the return air holes are formed in the pressure side walland the suction side wall and in the zigzag shaped main piece.
 7. Theimpingement cooling insert of claim 1, and further comprising: thepressure side wall and the suction side wall extend around both aforward side and an aft side of the zigzag shaped main piece with thepressure side wall secured to the suction side wall on the forward sideand the aft side.
 8. The impingement cooling insert of claim 7, andfurther comprising: a forward radial extending seal groove on theforward side; and, an aft radial extending seal groove on the aft side.